Tidy networkCurve shaders

Arrays for start/end position/angle, smaller centre position, dynamic
segment count based on max error, calculate distance in tessellation
evaluation, use start/end position directly to avoid rounding errors at
joins.

See https://schneide.blog/2025/05/21/calculating-the-number-of-segments-for-accurate-circle-rendering/

4 files changed, 52 insertions, 47 deletions

diff --git a/gfx/gl/shaders/networkCurve.geom b/gfx/gl/shaders/networkCurve.geom
index 1002fd4..4a5b3db 100644
--- a/gfx/gl/shaders/networkCurve.geom
+++ b/gfx/gl/shaders/networkCurve.geom
@@ -1,15 +1,17 @@
 #version 460 core
 
+layout(lines) in;
+layout(triangle_strip, max_vertices = 10) out;
+
 flat in ivec3 pos[];
 flat in mat2 rot[];
 flat in float tpos[];
+flat in float dist[];
 
-layout(lines) in;
-layout(triangle_strip, max_vertices = 10) out;
 include(`networkCommon.glsl')
 
 void
 main()
 {
-	doSeg(segDist(pos[0], pos[1]), pos[0], pos[1], tpos[0], tpos[1], rot[0], rot[1]);
+	doSeg(min(dist[0], dist[1]), pos[0], pos[1], tpos[0], tpos[1], rot[0], rot[1]);
 }
diff --git a/gfx/gl/shaders/networkCurve.tesc b/gfx/gl/shaders/networkCurve.tesc
index 4221e64..5a6e449 100644
--- a/gfx/gl/shaders/networkCurve.tesc
+++ b/gfx/gl/shaders/networkCurve.tesc
@@ -1,43 +1,37 @@
 #version 460 core
 
 layout(vertices = 1) out;
-flat in ivec3 apos[];
-flat in ivec3 bpos[];
-flat in ivec3 cpos[];
+
+flat in ivec3 pos[][2];
+flat in ivec2 cpos[];
 flat in float reps[];
-flat in float aangle[];
-flat in float bangle[];
+flat in float angles[][2];
 flat in float radius[];
 
-flat out ivec3 c_apos[];
-flat out ivec3 c_bpos[];
-flat out ivec3 c_cpos[];
+flat out ivec3 c_pos[][2];
+flat out ivec2 c_cpos[];
 flat out float c_reps[];
-flat out float c_aangle[];
-flat out float c_bangle[];
+flat out float c_angles[][2];
 flat out float c_radius[];
 
-int
-min2pow(float target)
+float
+segments()
 {
-	int x = 1;
-	while (x < target) {
-		x <<= 1;
-	}
-	return x;
+	const float arc = angles[gl_InvocationID][0] - angles[gl_InvocationID][1];
+	const float error = 100.;
+	const float diff = acos(1.f - (error / radius[gl_InvocationID]));
+	return clamp(arc / diff, arc, 180);
 }
 
 void
 main()
 {
-	c_apos[gl_InvocationID] = apos[gl_InvocationID];
-	c_bpos[gl_InvocationID] = bpos[gl_InvocationID];
+	c_pos[gl_InvocationID] = pos[gl_InvocationID];
 	c_cpos[gl_InvocationID] = cpos[gl_InvocationID];
 	c_reps[gl_InvocationID] = reps[gl_InvocationID];
-	c_aangle[gl_InvocationID] = aangle[gl_InvocationID];
-	c_bangle[gl_InvocationID] = bangle[gl_InvocationID];
+	c_angles[gl_InvocationID] = angles[gl_InvocationID];
 	c_radius[gl_InvocationID] = radius[gl_InvocationID];
 
 	gl_TessLevelOuter[0] = 1;
-	gl_TessLevelOuter[1] = min2pow(reps[gl_InvocationID]);
+	gl_TessLevelOuter[1] = segments();
 }
diff --git a/gfx/gl/shaders/networkCurve.tese b/gfx/gl/shaders/networkCurve.tese
index a02503c..82e6a13 100644
--- a/gfx/gl/shaders/networkCurve.tese
+++ b/gfx/gl/shaders/networkCurve.tese
@@ -1,17 +1,22 @@
 #version 460 core
+
 layout(isolines, equal_spacing, cw) in;
 
-flat in ivec3 c_apos[];
-flat in ivec3 c_bpos[];
-flat in ivec3 c_cpos[];
+uniform ivec3 viewPoint;
+
+flat in ivec3 c_pos[][2];
+flat in ivec2 c_cpos[];
 flat in float c_reps[];
-flat in float c_aangle[];
-flat in float c_bangle[];
+flat in float c_angles[][2];
 flat in float c_radius[];
 
 flat out ivec3 pos;
 flat out mat2 rot;
 flat out float tpos;
+flat out float dist;
+
+const float startTolerance = 1. / 200.;
+const float endTolerance = 1. - startTolerance;
 
 mat2
 getRot(float angle)
@@ -22,9 +27,19 @@ getRot(float angle)
 void
 main()
 {
-	float angle = mix(c_bangle[0], c_aangle[0], gl_TessCoord.x);
-	int height = int(mix(c_bpos[0].z, c_apos[0].z, gl_TessCoord.x)) - c_cpos[0].z;
+	const float angle = mix(c_angles[0][1], c_angles[0][0], gl_TessCoord.x);
 	rot = getRot(angle);
+	if (gl_TessCoord.x < startTolerance) {
+		pos = c_pos[0][1];
+	}
+	else if (gl_TessCoord.x > endTolerance) {
+		pos = c_pos[0][0];
+	}
+	else {
+		const int height = int(mix(c_pos[0][1].z, c_pos[0][0].z, gl_TessCoord.x));
+		pos = ivec3(c_cpos[0] + ivec2(rot * vec2(c_radius[0], 0)), height);
+	}
+
 	tpos = c_reps[0] * gl_TessCoord.x;
-	pos = c_cpos[0] + ivec3(rot * vec2(c_radius[0], 0), height);
+	dist = length(vec3(viewPoint - pos));
 }
diff --git a/gfx/gl/shaders/networkCurve.vert b/gfx/gl/shaders/networkCurve.vert
index 9cf149b..7e363d3 100644
--- a/gfx/gl/shaders/networkCurve.vert
+++ b/gfx/gl/shaders/networkCurve.vert
@@ -1,29 +1,23 @@
 #version 460 core
 
-layout(location = 0) in ivec3 v_apos;
-layout(location = 1) in ivec3 v_bpos;
+layout(location = 0) in ivec3 v_pos[2];
 layout(location = 2) in ivec3 v_centre;
 layout(location = 3) in float v_reps;
-layout(location = 4) in float v_aangle;
-layout(location = 5) in float v_bangle;
+layout(location = 4) in float v_angles[2];
 layout(location = 6) in float v_radius;
 
-flat out ivec3 apos;
-flat out ivec3 bpos;
-flat out ivec3 cpos;
+flat out ivec3 pos[2];
+flat out ivec2 cpos;
 flat out float reps;
-flat out float aangle;
-flat out float bangle;
+flat out float angles[2];
 flat out float radius;
 
 void
 main()
 {
-	apos = v_apos;
-	bpos = v_bpos;
-	cpos = v_centre;
+	pos = v_pos;
+	cpos = v_centre.xy;
 	reps = v_reps;
-	aangle = v_aangle;
-	bangle = v_bangle;
+	angles = v_angles;
 	radius = v_radius;
 }